Formulation for evaluating tensile strength of girth weld joint of linepipe with softened HAZ under internal pressure

Abstract

Buried gas pipeline is subjected to a large axial load due to earthquake-induced ground flow. The deformability of the pipeline depends on the strength of the girth weld joint. Since the heat-affected zone (HAZ) of tempered steels is locally softened due to the heat input of girth welding, the strength of the girth weld may be affected by softened HAZ. In addition, as for gas pipeline, the effect of internal pressure on the strength of the girth weld joint should be considered. Therefore, this paper proposes a tensile strength evaluation formula for girth weld joint with softened HAZ under internal pressure. The formula is developed by modifying the existing tensile strength evaluation formula of the wide plate of weld joint with softened HAZ, considering the effect of internal pressure using the elastoplastic finite element analysis. In this modification, the effect of both internal pressures on the apparent tensile strength of pipe material and the shrinkage behaviour of pipe material are focused on. Furthermore, the validity of the modified formula is demonstrated by conducting full-scale pipe tension tests.